Aging is characterized by a host of changes in metabolic variables which have profound effects on disease development and on survival. The BLSA provides the opportunity to conduct analyses on these variables to relate them to other characteristics of the individual, and to analyze for long-term effects of these complex interactions. Variables which are potentially alterable by changes in life style characteristics (diet, body-weight, activity level) are of especial importance in this respect. Age-specific normative data are required and can only be determined rationally by analyses such as these. Dietary diary information has been obtained on 600 men and women. This has provided an important update on secular changes in the diet since the 1961-1976 dietary analyses were published. The dietary trends seen from the 1960s to the 1970s have continued into the 1980s. Total caloric intake decreased, calories from fat were partially replaced by calories from carbohydrate, the polyunsaturated; saturated fatty acid ratio increased further and cholesterol intake continued to fall. Crude fiber intake rose. These favorable trends were seen in all age groups from young to middle-aged and old adults. Collaborative studies with NCI scientists showed that remote dietary habits (10- 14 years in the past) could be obtained by personal interview with remarkable validity. BLSA men who had provided 7-day dietary diaries in 1971-1975 were contacted in 1985. The use of a self- administered dietary questionnaire will provide less satisfactory data unless personal instruction and follow-up call-backs are included in the process. Interestingly, age itself did not influence the accuracy of the results. These results indicate that long-term dietary histories - an important methodologic requirement for testing theories of the dietary causation of a number of important illnesses - can be obtained with remarkable accuracy.